The present invention relates to a control method for compensating changes in the SRS-induced power exchange when connecting channels into, and disconnecting them from, a continuous optical data transmission path of a WDM system by influencing the tilting of the spectrum. Furthermore, the present invention relates to an optical data transmission path having a WDM system with a multiplicity of data transmission channels of different frequencies with at least one multiplexer, arranged at the beginning, for combining the data transmission channels, one demultiplexer arranged at the end, for separating the data transmission channels, and at least one path section, arranged therebetween, having capabilities for determining and compensating the spectral tilting of transmitted data signals.
It is known that stimulated Raman scattering (SRS) leads to a power exchange between the individual wavelength channels of a wavelength multiplex system (WDM system). Channels with relatively large wavelengths experience an increase in their medium power here, while the average power of channels with relatively small wavelengths decreases. This effect of SRS can be counteracted in the steady state of a data transmission path with WDM system by “tilting” the gain spectrum of an erbium-doped fiber amplifier (EDFA), for example using mechanically controllable filters, as is known from the U.S. Pat. No. 5,847,862. However, a problem here is the time when channels are connected or disconnected during operation.
Another is the failure of individual channels. Both the controllable filters and the erbium-doped fiber amplifiers are too slow in their reaction in order to be able to react quickly to the rapid intensity changes resulting from the connection and disconnection of individual channels or of a number of channels. Thus, during the transmission of data, time periods in which the noise/signal ratio is too low and the bit error rate of at least individual channels rises occur repeatedly. This leads then to a reduced data rate in these data transmission paths.
An object of the present invention is, therefore, to develop a method and a device which permit quicker compensation of the tilting of the spectrum during the connection or disconnection of channels, or when channels fail, in a data transmission path with WDM system.